Re: [GSoC RFC PATCH v4 2/4] repo: add the field references.format

> git-repo-info.
> 
> The flag `--show-ref-format` from git-rev-parse is used for retrieving
> the reference format (i.e. `files` or `reftable`). This way, it is
> used for querying repository metadata, fitting in the purpose of
> git-repo-info.
> 
> Then, add a new field `references.format` to the repo-info subcommand
> containing that information.
> 
> Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
> Helped-by: Junio C Hamano <gitster@pobox.com>
> Helped-by: Justin Tobler <jltobler@gmail.com>
> Mentored-by: Karthik Nayak <karthik.188@gmail.com>
> Mentored-by: Patrick Steinhardt <ps@pks.im>
> Signed-off-by: Lucas Seiki Oshiro <lucasseikioshiro@gmail.com>
> ---
>  Documentation/git-repo.adoc |  4 ++
>  builtin/repo.c              | 92 +++++++++++++++++++++++++++++++++++--
>  t/meson.build               |  1 +
>  t/t1900-repo.sh             | 47 +++++++++++++++++++
>  4 files changed, 140 insertions(+), 4 deletions(-)
>  create mode 100755 t/t1900-repo.sh
> 
> diff --git a/Documentation/git-repo.adoc b/Documentation/git-repo.adoc
> index 6f8fe3f6ea..b7af6f45a4 100644
> --- a/Documentation/git-repo.adoc
> +++ b/Documentation/git-repo.adoc
> @@ -45,6 +45,10 @@ INFO KEYS
>  The set of data that `git repo` can return is grouped into the following
>  categories:
>  
> +`references`::
> +Reference-related data:
> +* `format`: the reference storage format, either `files` or `reftable`.
> +
>  SEE ALSO
>  --------
>  linkgit:git-rev-parse[1]
> diff --git a/builtin/repo.c b/builtin/repo.c
> index a1787a3cc5..dcda0d6d61 100644
> --- a/builtin/repo.c
> +++ b/builtin/repo.c
> @@ -1,11 +1,95 @@
>  #include "builtin.h"
>  #include "parse-options.h"
> +#include "strbuf.h"
> +#include "refs.h"
>  
> -static int repo_info(int argc UNUSED,
> -		     const char **argv UNUSED,
> +typedef void add_field_fn(struct strbuf *buf, struct repository *repo);
> +
> +struct field {
> +	const char *key;
> +	add_field_fn *add_field_callback;
> +};
> +
> +static void add_string(struct strbuf *buf,
> +		       const char *key, const char *value)
> +{
> +	strbuf_addf(buf, "%s\n%s%c", key, value, '\0');
> +}